Alien : The Space Jockey design as it is in Alien

a) In the derelict vessel in the movie Alien, the remains of a huge alien pilot are found fossilised into it's chair. Ridley Scott told Giger that he wanted to show the pilot of the space vessel and he should be installed in his operating position, sitting in front of his levers and his chair should be at the centre of this architectual curve that would be the pilots chamber.

c) The actual construction was designed by Giger and sculpted by him with the help of Peter Voysey and Brian Muir. and finally Giger painted it as well. Brian Muir remembers that Giger actually told them that the pilot and the cockpit were to be as one as if merged together. The Space Jockey was modeled in clay, and then cast in clear resin. The remainder of the structure and the telescope were carved in polystyrene and applied to a wooden armature. Giger was very pleased with the final result of this character in his chair.

Source Quotes

Ridley Scott: J'ai simplement dit à Giger que je voulais montrer le pilote de vaisseau, et qu'il devait être encore installé à son poste de commande, assis devant ses manettes, et que son fauteuil devait se trouver au centre de cette architecture courbe.(Ecran Fantastique Hors Serie #20, 2012, p13)English TranslationRidley Scott: I just told Giger that I wanted to show the vessel's pilot, and should be already installed in its operating position, sitting in front of his levers, and his chair should be at the center of this architecture curve.

Brian Muir: "The jockey was modeled in clay, and then cast in clear resin. When finished it stood a remarkable 28
feet tall. Although Giger struggled with some of the more
frustrating-elements of the film making process, he was pleased with our
work and I found him to be a very pleasant man"(Scifi Now #52 2011, p115 & In the shadow of Vader by Brian Muir, p37)